The cell type responsible for resistance to tolerance induction by bovine gamma-globulin will be studied in a number of inbred mouse strains. In vitro tests of function of a macrophage-like cell will be correlated with in vivo behavior. Studies on various F1 and parental backcross offspring will be used to determine the nature of the genetic control of this phenomenon. An attempt will be made to determine the nature of receptors on T- cells by using an anti-idiotype serum directed against antibody specific for the same determinant toward which T cells respond to give a hapten- specific delayed sensitivity. The class of lymphocyte responsible for initiating the cutaneous basophil hypersensitivity reaction will be studied by use of specific lymphocyte mitogen, specific antisera and passive transfer studies with various cell preparations.